Many communication systems utilize high performance cables normally having four pairs or more that typically consist of two twisted pairs transmitting data and two receiving data as well as the possibility of four or more pairs multiplexing in both directions. A twisted pair is a pair of conductors twisted about each other. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs. High-speed data communications media in current usage includes pairs of wire twisted together to form a balanced transmission line. Optical fiber cables may include such twisted pairs or replace them altogether with optical transmission media (fiber optics).
When twisted pairs are closely placed, such as in a communications cable, electrical energy may be transferred from one pair of a cable to another. Energy transferred between conductor pairs is undesirable and referred to as crosstalk. The Telecommunications Industry Association and Electronics Industry Association have defined standards for crosstalk, including TIA/EIA-568A. The International Electrotechnical Commission has also defined standards for data communication cable crosstalk, including ISO/EC 11801. One high-performance standard for 100 MHz cable is ISO/IEC 11801, Category 5. Additionally, more stringent standards are being implemented for higher frequency cables including Category 6 and Category 7, which includes frequencies of 200 and 600 MHz, respectively. Industry standards cable specifications and known commercially available products are listed in Table 1.
TABLE 1INDUSTRY STANDARD CABLE SPECIFICATIONSANIXTERANIXTERTIA CAT 6XP6XP7ALL DATA ATDRAFT 10R3.00XPR3.00XP100 MHzTIA CAT 5eNov. 15, 2001November 2000November 2000MAX TEST100MHz250MHz250MHz350MHzFREQUENCYATTENTUATION22.0db19.8db21.7db19.7dbPOWER SUM32.3db42.3db34.3db44.3dbNEXTACR13.3db24.5dbPOWER SUM10.3db22.5db12.6db23.6dbACRPOWER SUM20.8db24.8db23.8db25.8dbELFEXTRETURN LOSS20.1db20.1db21.5db22.5db
TABLE 2CLASSES OF REACTION TO FIRE PERFORMANCE FOR POWER,CONTROL AND COMMUNICATION CABLES (*)ClassTest method(s)Classification criteria (1)Additional classificationACEN ISO 1716PCS ≦2.0 MJ · kg−1 (2)—BCEN 50266-2-x (3)FS ≦2.0 m; andSmoke production (5) andAndTHR1200s ≦30 MJ; andFlaming droplets/particles (7);Peak RHR ≦60 kW; andAcidity/Corrosivity (8)FIGRA ≦150 W · s−1EN 50265-2-1H ≦425 mmCCEN 50266-2-y (4)FS ≦2.0 m; andSmoke production (6) andAndTHR600s ≦15 MJ; andFlaming droplets/particles (7);Peak RHR ≦60 kW; andAcidity/Corrosivity (8)FIGRA ≦150 W · s−1EN 50265-2-1H ≦425 mmDCEN 50266-2-y (4)FS ≦2.5 m; andSmoke production (6) andAndTHR600s ≦35 MJ; andFlaming droplets/particles (7);Peak RHR ≦200 kW; andAcidity/Corrosivity (8)FIGRA ≦250 W · s−1EN 50265-2-1H ≦425 mmECEN 50265-2-1H ≦425 mmFlaming droplets/particles (7);Acidity/Corrosivity (8)FCNo performance determined(1) Symbols used: PCS—gross calorific potential; FS—flame spread; THR—total heat release, RHR—rate of heat release; FIGRA—fire growth rate; TSP—total smoke production; SPR—smoke production rate; H—flame spread.(2) Mineral insulated cables without a polymeric sheath, as defined in HD 50 386, are deemed to satisfy the Class AC requirement without the need for testing.(3) EN 50266-2-4 modified on the basis of FIPEC scenario 2 and to include heat release and smoke measurements.(4) EN 50266-2-4 modified to include heat release and smoke measurements.(5) EN 50266-2-x: s1 = TSP ≦100 m2 and Peak SPR ≦0.25 m2/s; s2 = TSP ≦200 m2 and Peak SPR ≦0.5 m2/s; s3 = not s1 or s2.(6) EN 50266-2-y: s1 = TSP ≦50 m2 and Peak SPR ≦0.25 m2/s; s2 = TSP ≦100 m2 and Peak SPR ≦0.5 m2/s; s3 = not s1 or s2.(7) EN 50265-2-1 (mod.): d0 = No flaming droplets/particles; d1 = No flaming droplets/particles persisting longer than x s; d2 = not d0 or d1.(8) EN 50267-2-3: a1 = conductivity <2.5 μS/mm and pH > 4.3; a2 = conductivity <10 μS/mm and pH > 4.3; a3 = not a1 or a2. No declaration = No Performance Determined.(*) This Classification table applies to power, control and communication cables designed for use in buildings and other civil engineering works, with a voltage rating up to 1000 V for alternating current and 1500 V for direct current. It does not cover control and power circuits covered under the Machinery Directive 98/37/EC or lifts Directive 95/16/EC
In conventional cable, each twisted pair of conductors for a cable has a specified distance between twists along the longitudinal direction. That distance is referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist direction. Such close spacing increases the amount of undesirable cross-talk that occurs. Therefore, in many conventional cables, each twisted pair within the cable has a unique pair lay in order to increase the spacing between pairs and thereby to reduce the cross-talk between twisted pairs of a cable. Twist direction may also be varied. Along with varying pair lays and twist directions, individual solid metal or woven metal air shields can be used to electro-magnetically isolate pairs from each other or isolate the pairs from the cable jacket.
Shielded cable, although exhibiting better cross-talk isolation, is more difficult, time consuming and costly to manufacture, install, and terminate. Individually shielded pairs must generally be terminated using special tools, devices and techniques adapted for the job, also increasing cost and difficulty.
One popular cable type meeting the above specifications is Unshielded Twisted Pair (UTP) cable. Because it does not include shielded pairs, UTP is preferred by installers and others associated with wiring building premises, as it is easily installed and terminated. However, UTP fails to achieve superior cross-talk isolation such as required by the evolving higher frequency standards for data and other state of the art transmission cable systems, even when varying pair lays are used.
Some cables have used supports in connection with twisted pairs. These cables, however, suggest using a standard “X”, or “+” shaped support, hereinafter both referred to as the “X” support. Protrusions may extend from the standard “X” support. The protrusions of these prior inventions have exhibited substantially parallel sides.
The document, U.S. Pat. No. 3,819,443, hereby incorporated by reference, describes a shielding member comprising laminated strips of metal and plastics material that are cut, bent, and assembled together to define radial branches on said member. It also describes a cable including a set of conductors arranged in pairs, said shielding member and an insulative outer sheath around the set of conductors. In this cable the shielding member with the radial branches compartmentalizes the interior of the cable. The various pairs of the cable are therefore separated from each other, but each is only partially shielded, which is not so effective as shielding around each pair and is not always satisfactory.
The solution to the problem of twisted pairs lying too closely together within a cable is embodied in three U.S. Pat. No. 6,150,612 to Prestolite, U.S. Pat. No. 5,952,615 to Filotex, and U.S. Pat. No. 5,969,295 to CommScope incorporated by reference herein, as well as an earlier similar design of a cable manufactured by Belden Wire & Cable Company as product number 1711A. The prongs or splines in the Belden cable provide superior crush resistance to the protrusions of the standard “X” support. The superior crush resistance better preserves the geometry of the pairs relatives to each other and of the pairs relative to the other parts of the cables such as the shield. In addition, the prongs or splines in this invention preferably have a pointed or slightly rounded apex top which easily accommodates an overall shield. These cables include four or more twisted pair media radially disposed about a “+”-shaped core. Each twisted pair nests between two fins of the “+”-shaped core, being separated from adjacent twisted pairs by the core. This helps reduce and stabilize crosstalk between the twisted pair media. U.S. Pat. No. 5,789,711 to Belden describes a “star” separator that accomplishes much of what has been described above and is also herein incorporated by reference.
However, these core types can add substantial cost to the cable, as well as excess material mass which forms a potential fire hazard, as explained below, while achieving a crosstalk reduction of typically 3 dB or more. This crosstalk value is based on a cable comprised of a fluorinated ethylene-propylene (FEP) conductors with PVC jackets as well as cables constructed of FEP jackets with FEP insulated conductors. Cables where no separation between pairs exist will exhibit smaller cross-talk values. When pairs are allowed to shift based on “free space” within the confines of the cable jacket, the fact that the pairs may “float” within a free space can reduce overall attenuation values due to the ability to use a larger conductor to maintain 100 ohm impedance. The trade-off with allowing the pairs to float is that the pair of conductors tend to separate slightly and randomly. This undesirable separation contributes to increased structural return loss (SRL) and more variation in impedance. One method to overcome this undesirable trait is to twist the conductor pairs with a very tight lay. This method has been proven impractical because such tight lays are expensive and greatly limits the cable manufacturer's throughput and overall production yield. An improvement included by the present invention to structural return loss and improved attenuation is to provide grooves within channels for conductor pairs such that the pairs are fixedly adhered to the walls of these grooves or at least forced within a confined space to prevent floating simply by geometric configuration. This configuration is both described herewithin and referenced in U.S. patent application Ser. No. 09/939,375, filed Aug. 25, 2001. A “rifling” or “ladder-like” separator design also contributes to improved attenuation, power sum NEXT (near end cross talk), power sum ACR (attenuation cross-talk ratio) and ELFEXT (equal level far end cross-talk) by providing for better control of spacing of the pairs, adding more air-space, and allowing for “pair-twinning” at different lengths. Additional benefits include reduction of the overall material mass required for conventional spacers, which contributes to flame and smoke reduction.
In building designs, many precautions are taken to resist the spread of flame and the generation of and spread of smoke throughout a building in case of an outbreak of fire. Clearly, the cable is designed to protect against loss of life and also minimize the costs of a fire due to the destruction of electrical and other equipment. Therefore, wires and cables for building installations are required to comply with the various flammability requirements of the National Electrical Code (NEC) in the U.S. as well as International Electrotechnical Commission (EIC) and/or the Canadian Electrical Code (CEC).
Cables intended for installation in the air handling spaces (i.e. plenums, ducts, etc.) of buildings are specifically required by NEC/CEC/EEC to pass the flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FT6. The UL-910 and the FT6 represent the top of the fire rating hierarchy established by the NEC and CEC respectively. Also important are the UL 1666 Riser test and the EC 60332-3C and D flammability criteria. Cables possessing these ratings, generically known as “plenum” or “plenum rated” or “riser” or “riser rated”, may be substituted for cables having a lower rating (i.e. CMR, CM, CMX, FT4, FTI or their equivalents), while lower rated cables may not be used where plenum or riser rated cables are required.
Cables conforming to NEC/CEC/IEC requirements are characterized as possessing superior resistance to ignitability, greater resistant to contribute to flame spread and generate lower levels of smoke during fires than cables having lower fire ratings. Often these properties can be anticipated by the use of measuring a Limiting Oxygen Index (LOI) for specific materials used to construct the cable. Conventional designs of data grade telecommunication cable for installations in plenum chambers have a low smoke generating jacket material, e.g. of a specially filled PVC formulation or a fluoropolymer material, surrounding a core of twisted conductor pairs, each conductor individually insulated with a fluorinated insulation layer. Cable produced as described above satisfies recognized plenum test requirements such as the “peak smoke” and “average smoke” requirements of the Underwriters Laboratories, Inc., UL910 Steiner tunnel test and/or Canadian Standards Association CSA-FT6 (Plenum Flame Test) while also achieving desired electrical performance in accordance with EIA/TIA-568A for high frequency signal transmission.
While the above described conventional cable, including the Belden 1711A cable design, due in part to their use of fluorinated polymers, meets all of the above design criteria, the use of fluorinated polymers is extremely expensive and may account for up to 60% of the cost of a cable designed for plenum usage. A solid core of these communications cables contributes a large volume of fuel to a potential cable fire. Forming the core of a fire resistant material, such as with FEP (fluorinated ethylene-propylene), is very costly due to the volume of material used in the core, but it should help reduce flame spread over the 20-minute test period. Reducing the mass of material by redesigning the core and separators within the core is another method of reducing fuel and thereby reducing smoke generation and flame spread. For the commercial market in Europe, low smoke fire retardant polyolefin materials have been developed that will pass the EN (European Norm) 502666-Z-X Class B relative to flame spread, total heat release, related heat release, and fire growth rate. Prior to this inventive development, standard cable constructions requiring the use of the aforementioned expensive fluorinated polymers, such as FEP, would be needed to pass this rigorous test. Using low smoke fire retardant polyolefins for specially designed separators used in cables that meet the more stringent electrical requirements for Categories 6 and 7 and also pass the new norm for flammability and smoke generation is a further subject of this invention.
Solid flame retardant/smoke suppressed polyolefins may also be used in connection with fluorinated polymers. Commercially available solid flame retardant/smoke suppressed polyolefin compounds all possess dielectric properties inferior to that of FEP and similar fluorinated polymers. In addition, they also exhibit inferior resistance to burning and generally produce more smoke than FEP under burning conditions. A combination of the two different polymer types can reduce costs while minimally sacrificing physio-chemical properties. An additional method that has been used to improve both electrical and flammability properties includes the irradiation of certain polymers that lend themselves to crosslinking. Certain polyolefins are currently in development that have proven capable of replacing fluoropolymers for passing these same stringent smoke and flammability tests for cable separators, also known as “cross-webs”. Additional advantages with the polyolefins are reduction in cost and toxicity effects as measured during and after combustion.
A high performance communications data cable utilizing twisted pair technology must meet exacting specification with regard to data speed, electrical, as well as flammability and smoke characteristics. The electrical characteristics include specifically the ability to control impedance, near-end cross-talk (NEXT), ACR (attenuation cross-talk ratio) and shield transfer impedance. A method used for twisted pair data cables that has been tried to meet the electrical characteristics, such as controlled NEXT, is by utilizing individually shielded twisted pairs (ISTP). These shields insulate each pair from NEXT.
Data cables have also used very complex lay techniques to cancel E and B (electric and magnetic fields) to control NEXT. In addition, previously manufactured data cables have been designed to meet ACR requirements by utilizing very low dielectric constant insulation materials. Use of the above techniques to control electrical characteristics have inherent problems that have lead to various cable methods and designs to overcome these problems.
Recently, the development of “high-end” electrical properties for Category 6 and 7 cables has increased the need to determine and include power sum NEXT (near end crosstalk) and power sum ELFEXT (equal level far end crosstalk) considerations along with attenuation, impedance, and ACR values. These developments have necessitated the development of more highly evolved separators that can provide offsetting of the electrical conductor pairs so that the lesser performing electrical pairs can be further separated from other pairs within the overall cable construction.
Recent and proposed cable standards are increasing cable maximum frequencies from 100-200 MHz to 250-700 Mhz. The maximum upper frequency of a cable is that frequency at which the ACR (attenuation/cross-talk ratio) is essentially equal to 1. Since attenuation increases with frequency and cross-talk decreases with frequency, the cable designer must be innovative in designing a cable with sufficiently high cross-talk. This is especially true since many conventional design concepts, fillers, and spacers may not provide sufficient cross-talk at the higher frequencies.
Current separator designs must also meet the UL 910 flame and smoke criteria using both fluorinated and non-fluorinated jackets as well as fluorinated and non-fluorinated insulation materials for the conductors of these cable constructions. In Europe, the trend continues to be use of halogen free insulation for all components, which also must meet stringent flammability regulations.
Individual shielding is costly and complex to process. Individual shielding is highly susceptible to geometric instability during processing and use. In addition, the ground plane of individual shields, 360° in ISTP's—individually shielded twisted pairs is also an expensive process. Lay techniques and the associated multi-shaped anvils of the present invention to achieve such lay geometries are also complex, costly and susceptible to instability during processing and use. Another problem with many data cables is their susceptibility to deformation during manufacture and use. Deformation of the cable geometry, such as the shield, also potentially severely reduces the electrical and optical consistency.
Optical fiber cables exhibits a separate set of needs that include weight reduction (of the overall cable), optical functionality without change in optical properties and mechanical integrity to prevent damage to glass fibers. For multi-media cable, i.e. cable that contains both metal conductors and optical fibers, the set of criteria is often incompatible. The use of the present invention, however, renders these often divergent set of criteria compatible. Specifically, optical fibers must have sufficient volume in which the buffering and jacketing plenum materials (FEP and the like) covering the inner glass fibers can expand and contract over a broad temperature range without restriction, for example −40 C to 80 C experienced during shipping. It has been shown by Grune, et. al., among others, that cyclical compression and expansion directly contacting the buffered glass fiber causes excess attenuation light loss (as measured in dB) in the glass fiber. The design of the present invention allows for designation and placement of optical fibers in clearance channels provided by the support-separator, having multi-anvil shaped profiles. It would also be possible to place both glass fiber and metal conductors in the same designated clearance channel if such a design is required. In either case the forced spacing and separation from the cable jacket (or absence of a cable jacket) would eliminate the undesirable set of cyclical forces that cause excess attenuation light loss. In addition, fragile optical fibers are susceptible to mechanical damage without crush resistant members (in addition to conventional jacketing). The present invention also addresses this problem.
The need to improve the cable and cable separator design, reduce costs, and improve both flammability and electrical properties continues to exist.